1. Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus for polishing a planar workpiece such as a semiconductor wafer to a flat mirror finish.
2. Description of the Prior Art
As semiconductor devices become finer and more highly integrated in recent years, circuit interconnections become thinner and the distances between those interconnections also become smaller. Photolithographic processes for producing circuits in integrated semiconductor devices of that type require a flat image-focusing plane for a stepper device because the depth of focus of the light beam is narrow. Therefore, it is necessary to planarize the s of semiconductor wafers. One proposal to planarize semiconductor wafers to a flat finish has been to use a chemical-mechanical polishing (CMP) apparatus for polishing a semiconductor wafer. The CMP apparatus polishes the semiconductor wafer by pressing the semiconductor wafer held by a carrier against an abrasive cloth while supplying an abrasive solution containing abrasive grain to the abrasive cloth which is attached to a rotating turntable.
One such CMP polishing unit comprises an abrasive table rotatable in a plane, and a carrier for pressing a surface of a workpiece to be polished against the abrasive table. To the polishing unit, there are added a storage device for storing workpieces, a cleaning device for cleaning the workpieces which have been polished by the polishing unit, a reversing device disposed adjacent to the storage device, and a delivery device for delivering workpieces between the storage device, the cleaning device, and the reversing device.
FIG. 7 of the accompanying drawings shows a conventional CMP apparatus. As shown in FIG. 7, the conventional CMP apparatus comprises: a pair of storage devices 100a, 100b for storing workpieces; a pair of polishing units 106a, 106b each having a turntable 102 and a top ring 104; a plurality of cleaning devices 108a-108d for cleaning and drying the workpieces which have been polished by the polishing units 106a, 106b; a delivery device 110 for delivering workpieces between the storage devices 100a, 100b, the polishing units 106a, 106b, and the cleaning devices 108a-108d; and a pair of reversing devices 112a, 112b for reversing an orientation of each of the workpieces. The components of the polishing apparatus are arranged in a chamber defined by a frame in the form of a rectangular parallelepiped. The components are arranged in view of an overall flow of the processing operation and the direction in which workpieces are delivered. The components are enclosed by a single cover forming a chamber which is air-conditioned such that air flows downwardly in the chamber.
Since the polishing apparatus shown in FIG. 7 has two polishing units, it can be used to polish compound semiconductor wafers in multiple stages using different abrasive solutions while preventing compound semiconductor wafers from being contaminated by an abrasive solution used in a previous stage. Consequently, a reduction in the quality and yield of polished semiconductor wafers is avoided. If the polishing apparatus shown in FIG. 7 is used to polish semiconductor wafers in a single stage, then semiconductor wafers may be polished simultaneously by the two polishing units, thereby increasing throughput.
In the conventional polishing apparatus, the various components are accommodated in one chamber. Therefore, air may flow between a polishing process having a relatively low requirement for clean air and a final cleaning process having a relatively high requirements for clean air. For example, small particles which may comprise splashed abrasive solution and removed wafer material tend to flow from a polishing unit to a cleaning device, contaminating the cleaning device. Furthermore, because those semiconductor wafers which have been polished, cleaned, and dried are delivered to the storage devices 100a, 100b by the delivery device 110, when the delivery device 110 is contaminated, then the semiconductor wafers that are carried by the delivery device 110 are also contaminated. If the requirement for clean air in the chamber as a whole must be increased in order to avoid undesirable contamination, then the air-conditioning unit used needs to have an increased capability. This results in an increase in the cost of the facility and the operation cost. One solution would be to partition the various different processes into compartments. However, the partitioned processes could not easily be accessed by human operators so that it would become difficult to inspect and service the components in the compartments.